1. Field of the Invention
The present invention generally relates to an etching method for silicon substrates. More particularly, the present invention relates to an etching method for silicon substrates used for forming thinned portions of semiconductor sensors, e.g., a pressure sensor and an acceleration sensor.
2. Related Arts
In the conventional technique of manufacturing semiconductor pressure sensors, anisotropic etching using KOH is used for forming a thin diaphragm on a portion of a (110)-oriented silicon substrate, i.e., the (110)-oriented silicon substrate is etched by KOH through time control. However, due to the nature of the (110)-oriented silicon, this method results in the rough etching surface which causes unevenness to the characteristics of semiconductor pressure sensors. For this reason, there has been a need to smooth the etching surface.
As a solution to this problem, a SiO.sub.2 (SP--SiO.sub.2) film formed by the spattering method is provided on the etching surface on which a diaphragm has been formed as disclosed in the Journal of NIPPONDENSO Technical Disclosure No. 88-002, published on Jan. 15, 1993.
However, this method of providing the SP--SiO.sub.2 film requires another component material in addition to the silicon substrate and additional processes. Furthermore, even if electrochemical etching is used for etching the (110)-oriented silicon surface like etching a (100)-oriented silicon surface, the resultant etching surface is rough.